Power line communication or power line carrier (PLC) is a system for carrying data on a conductor also used for electric power transmission. A wide range of power line communication technologies are needed for different applications, ranging from home automation to Internet access.
Electrical power is transmitted over long distances using high voltage transmission lines, distributed over medium voltages, and used inside buildings at lower voltages. Hence, electrical power grids allow for relatively low cost communication over long distances. Full- and half-duplex systems (both one-way and two-way systems) have been successfully used for decades for purposes such as automatic remote meter readings.
Power line communications systems operate by impressing a modulated carrier signal on a wiring system. Different types of power line communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power distribution system was originally intended for transmission of AC power at typical frequencies of 50 Hz or 60 Hz, power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications. Data rates and distance limits vary widely over many power line communication standards. Low frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.
Narrowband power line communications began soon after electrical power supply became widespread. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes, and this continues. Consumer products such as baby alarms have been available at least since 1940. In the 1930's, ripple carrier signaling was introduced on the medium (10-20 kV) and low voltage (240/415 V) distribution systems. For many years, the search continued for a low cost bi-directional technology suitable for applications such as remote meter reading. The EDF (French power utility) prototyped and standardized a system called “spread frequency shift keying” or S-FSK. (See IEC 61334.) This system is now a simple, low-cost system with a long history. However, it has a very slow transmission rate, between 200 and 800 bits per second. In the 1970's, the Tokyo Electric Power Co. ran experiments that reported successful bi-directional operation with several hundred units. Since the mid-1980's, there has been a surge of interest in using the potential of digital communications techniques and digital signal processing. The drive is to produce a reliable system that is cheap enough to be widely installed and able to compete cost effectively with wireless solutions.
Applications of mains communications vary enormously, as would be expected of such a widely available medium. One natural application of narrow band power line communication is the control and telemetry of electrical equipment such as meters, switches, heaters and domestic appliances. A number of active developments are considering such applications from a systems point of view, such as demand side management wherein domestic appliances would intelligently co-ordinate their use of resources, for example limiting peak loads. Control and telemetry applications include both ‘utility side’ applications, which involve equipment belonging to the utility company up to the domestic meter, and ‘consumer-side’ applications that involve equipment in the consumer's premises. Possible utility-side applications include automatic meter reading (AMR), dynamic tariff control, load management, load profile recording, credit control, pre-payment, remote connection, fraud detection and network management, and could be extended to include gas and water. A project of EDF, France includes demand management, street lighting control, remote metering and billing, customer specific tariff optimization, contract management, expense estimation and gas applications safety. Many specialized niche applications also exist that use the mains supply within the home as a convenient data link for telemetry. For example, in the UK and Europe a TV audience monitoring system uses power line communications as a convenient data path between devices that monitor TV viewing activity in different rooms in a home and a data concentrator that is connected to a telephone modem.
Several competing organizations have developed specifications, including the HomePlug Powerline Alliance, Universal Power line Association and HD-PLC Alliance. On December 2008, the ITU-T adopted recommendation G.hn/G.9960 as a standard for high-speed power line, coax and phone line communications. The National Energy Marketers Association was also involved in advocating for standards. IEEE P1901 is an IEEE working group developing the global standard for high-speed power line communications. In July 2009, the working group approved its “IEEE 1901 Draft Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications” as an IEEE draft standard for broadband over power lines defining medium access control and physical layer specifications. The IEEE 1901 Draft Standard was published by the IEEE in January 2010, and the final standard was approved on 30 Sep. 2010 and published on Feb. 1, 2011. NIST has included IEEE 1901, HomePlug AV and ITU-T G.hn as “Additional Standards Identified by NIST Subject to Further Review” for the smart grid in the United States. PRIME is one of the narrowband PLC technologies that has been widely adopted in Spain by utilities such as Iberdrola and Union Fenosa. Specifically, PRIME PLC system operation is defined in the draft Specification for Power Line Intelligent Metering Evolution incorporated by reference herein.
Increased use of PLC systems has generated the need for regularly obtaining data from all metered points in order to better control and operate the system. Specifically, there is a need for efficient selection of a switch node at the data concentrators, while also ensuring that the best possible node is chosen to be promoted as a switch node.